Samples of materials deposited on the exterior of nuclear fuel rods are needed by nuclear plant operators in order to perform material characteristic analysis. This material characteristic analysis allows the plant operators to understand the overall health of fuel assemblies placed in a nuclear reactor by looking at the types and mechanisms of degradation affecting the fuel assemblies. The material characteristic analysis identifies components within the reactor coolant system which may be failing or need attention.
Material that deposits or plates onto nuclear systems, such as CRUD upon fuel rods, can affects heat transfer characteristics of the components. In the case of CRUD, thicker layers of CRUD provide an insulating effect for the rod. The heat transfer capability of the fuel rods and associated assemblies, consequently, is decreased. The amounts of CRUD can vary significantly, thereby affecting the overall performance of fuel assemblies to such an extent that these fuel assemblies may need to be replaced/removed from service.
CRUD layers themselves are not homogeneous along their thickness. The material constituents of CRUD can vary greatly from the inner layer (inner surface) directly deposited on a specific heated surface, for example a zirconium fuel rod, to the outer layer (outer surface) still in contact with the reactor cooling water. To perform an accurate analysis of CRUD flakes, therefore, electronic microscope operators must determine whether the surface of the material being analyzed is an inner surface (i.e. the surface facing the center axis of the fuel rod) or an outer surface (i.e. the surface facing the coolant/moderator).
There is a need to determine an outer surface and an inner surface of a sample flake so that appropriate material analysis of the flake can be performed.